1. Field of the Invention
The present invention relates to propellant igniters and, more particularly pertains to a temperature-compensated, acceleration-activated igniter for use as a temporally accurate ignition means for traveling charges, rocket motors, multiple-staged combustion devices, and the like.
2. Description of the Prior Art
The accurate timing of the ignition of energetic materials is a critical consideration in many fields. For example, in many applications involving the use of combustible propellants, it is desirable to time ignition of a secondary charge in a safe, controlled fashion when the combustion products will materially contribute to the pressures generated by the main charge. In other applications, ignition events must be accurately controlled so as to occur in a precise time sequence. For instance, there are situations wherein certain ignition events for a gun-launched projectile need to occur after shot departure from the gun tube in order to be accurately timed. Also, the multiple staging of propellants is a well known desirable method of obtaining maximum interior ballistic performance.
Previous means employed by some to accomplish these timing functions included the use of deterrents on propellant grains or control of flame-spreading to inhibit or delay the initiation of combustion. Others have considered both solid and liquid propellants functioning as a "traveling charge". Still others have sought the adoption of available space to create the effect of a larger propellant chamber or to produce a delayed secondary charge. To date, such proposals primarily use or cite the potential adoption of delayed combustion stimulated by chemical means. All of these means, in turn, usually function more rapidly when they are initially hot as opposed to being initially cold. This phenomena is inherent in propellants: in the conventional 120 mm tank gun when firing high performance projectiles, the normal peak breech pressure at 70.degree. F. (21.degree. C.) is approximately 75,000 p.s.i. (517 MPa), while at hot (125.degree. F. or 51.7.degree. C.) and cold (-50.degree. F. or -46.degree. C.) initial temperatures, the peak breech pressure generated is normally 93,000 p.s.i. (641 MPa) and 54,000 p.s.i. (372 MPa), respectively. Because of this initial temperature effect, muzzle velocities of conventionally-propelled systems vary as much as 500 feet/sec. Muzzle velocity differences caused by secondary charges ignited by use of pyrotechnic delays would undoubtedly be more unless corrected.
Those concerned with the use of secondary charges as a means for increasing muzzle velocity recognize the potential dangers inherent in the hot ignition of such secondary charges. For example, the adoption of temperature-accelerated ignition trains for secondary propellant ignition in the vicinity of peak pressure could lead to serious system overpressures under hot conditions unless sufficient delay is included. The benefits of such secondary charges would be proportionately less effective if ignition were to be initiated at lower temperatures. Clearly, substantially lower muzzle velocities would be produced for the initially-cold case.
Consequently, for these and other reasons, those skilled in these arts recognize the need for improvements in propellant igniters that permit temporally accurate ignition of energetic materials on-board projectiles. The present invention fulfills this need.